Photoresist masks for patterning layers to fabricate electronic circuits are well-known. That technology is the basis for today's microcircuits. Briefly, positive or negative polymeric resists are used, involving the formation of a layer of resist on a surface, exposing the resist to radiation (visible, UV, X-ray, etc.) through a mask to cross-link (or unlink) portions of the resist, followed by removal of unwanted portions of the resist. The resist then serves as a mask for further processing steps, such as ion implantation, oxidation, metallization, and the like.
The area of molecular electronics is in its infancy. Developments in nanotechnology (critical dimension measured in nanometers) are directed to new generations of electronic circuitry, having much smaller dimensions than present technology can provide.
While a number of different approaches have been developed, one that is of current interest involves self-assembled wires, with at least one connector species between connecting pairs of wires to form a junction. The connector species comprises a bistable molecular switch. Such switches can be configured as, for example, crossbar memories and logic circuits. The investigations are reported, for example, by C. P. Collier et al., Science, Vol. 285, pp. 391–394 (16 Jul. 1999) and C. P. Collier et al., Science, Vol. 289, pp. 1172–1175 (18 Aug. 2000); see also U.S. Pat. No. 6,128,214, entitled “Molecular Wire Crossbar Memory”, issued Oct. 3, 2000, to P. J. Kuekes et al and U.S. Pat. No. 6,256,767, entitled “Demultiplexer for a Molecular Wire Crossbar Network (MWCN DEMUX)”, issued to P. J. Kuekes et al on Jul. 3, 2001.
The references in the foregoing paragraph deal with oxidation/reduction (“redox”) reactions involving, for example, rotaxanes, pseudo-rotaxanes, catenanes, and spiropyrans as the connector species. More recent work has shown that the connector species may comprise molecules that evidence an electric-field induced band gap change as a consequence of some mechanical action; see, e.g., application Ser. No. 09/823,195, filed Mar. 29, 2001, entitled “Bistable Molecular Mechanical Devices with a Band Gap Change Activated by an Electric Field for Electronic Switching, Gating, and Memory Applications”, and assigned to the same assignee as the present application. The molecular system employed as the connector species has an electric-field induced band gap change, and thus a change in its electrical conductivity, that occurs via one of the following mechanisms: (1) molecular conformation change (e.g., rotation of a part of the molecule with respect to another part of the molecule); (2) change of extended conjugation via chemical bonding change to alter the band gap (e.g., charge separation or recombination of the molecule); or (3) molecular folding or stretching. Nanometer-scale reversible electronic switches are thus provided that can be assembled easily to make cross-bar circuits, which provide memory, logic, and communication functions.
The patterning of nano-scale circuits with conventional photoresists presents a daunting task, and requires novel methods. Making and using resist by conventional means (especially in direct contact with the molecule, or connector species) could adversely alter the properties of the ultra-thin junction. Further, barrier materials between the molecule and the conventional resist could adversely alter the properties of the junction itself; for example, many metallic species could diffuse into or bind tightly with the molecule, becoming essentially unremovable/inseparable.
Polymer electronics on this thickness scale (nanometers) presents special problems (rotaxane studies by Collier et al, supra, are on the order of 100 Å or less). The present invention sidesteps the use of imprinting techniques and makes intermediate mask transfer unnecessary. The present invention is useful in both micrometer-scale and nanometer-scale devices.